54 ENZYMES OR SOLUBLE FERMENTS. 



shows that their composition approximates more nearly to that of 

 a proteid than of any other class of substances, and this is apparently 

 true even when they do not yield to any marked degree the reactions 

 (xanthoproteic, &c.) which are characteristic of a true proteid. 

 Ordinarily it is almost impossible to obtain an enzyme solution of any 

 considerable activity which is free from proteid reactions, and hence 

 many authors are inclined to regard these bodies as being really of 

 proteid nature. But this is a point which is as yet by no means 

 settled, as the following considerations show. The sole means at our 

 disposal of determining the presence of an enzyme is that of ascertain- 

 ing the change which it is able to bring about in other substances, and 

 since the activity of the enzymes is extraordinarily great, a minute 

 trace suffices to produce a most marked effect. From this it follows 

 that the purified enzymes which give distinct proteid reactions might 

 merely consist of very small quantities of a true non-proteid enzyme 

 adherent to or mixed with a residue of inert proteid material. Again 

 on the other hand it is similarly possible that the purified enzymes 

 which have been described as devoid of proteid reaction really consist 

 of some inert non-proteid material with which a trace of what is really 

 a true proteid enzyme is admixed, the amount of enzyme being too 

 small to yield any of the reactions characteristic of proteids. The 

 occurrence or absence of proteid reactions in a solution of an enzyme 

 cannot therefore settle the nature of the enzyme, and for similar 

 reasons a mere analysis of the separated enzyme is also inconclusive ; 

 the balance of recent opinion appears to be in favour of the view 

 that the enzymes are proteid in nature, but this is still an open 

 question. 



Many of the purified enzymes have been analysed and the results show in many 

 cases a percentage of carbon considerably lower than that of a true proteid. Kiibne's 

 purest trypsin had the following percentage composition C 47*22 48-09 ; H = 7'15 

 7-44; N = 12-59 13-41; S^l'73 1-86. For other analyses see Aug. Schmidt 1 , 

 Hiifner 2 , Earth 3 . But see also Wurtz 4 and Low 5 . 



The enzymes are possessed of certain properties more or less 

 common to them all by means of which they may be separated from 

 the tissues in which they primarily occur, and isolated from the 

 solutions thus obtained. Soluble in water, they may be precipitated 

 unchanged from this solution by the addition of an excess of absolute 

 alcohol. They may also in many cases be precipitated from their 



1 Inaug. Diss. Tubingen, 1871. 



2 Jn. f. prakt. Chem. N. F. Bd. v. (1872), S. 372. 



3 Ber. d. deutsch. Chem. Gesell. Jabrs. xi. (1878), S. 474. 



4 Compt. Rend. T. xc. (1880), p. 1379 ; xci. p. 787. 



5 Pfliiffer's Arch. Bd. xxvn. (1882k S. 203. 



